Gold alloy plating bath



United States Patent GOLD ALLOY PLATING BATH Charles R. Campana, New York, N. Y.

No Drawing. Application July 19, 1951, SerialNo. 237,667

2 Claims. (Cl. 204-43) My present invention relates to gold plating and to the baths used therefor, and aims to provide certain improvements therein.

In the electrodeposition of gold it has heretofore been necessary to deposit a plate of substantial thickness in order to provide a tarnish-proof and acid-proof, longwearing finish on the article. Hence, to provide a thick gold plate is costly.

Among the objects of my present invention are: (1) to provide a gold plate which is hard, long-wearing, tarnish-proof and acid-proof; (2) to provide a gold plate which is heavier yet less costly than conventional gold plate; (3) to provide a gold plate, the color of which can be readily controlled to match any other metal part, gold plate or gold having a predetermined carat of fineness; (4) to provide a gold plate which consists of a durable alloy of gold with a plurality of other metals; and (5) to provide a plating bath of novel composition from which a hard, long-wearing gold alloy plate can be deposited by a simple plating operation.

The foregoing and other objects of my invention not specifically enumerated I accomplish by employing a plating bath of novel composition which contains, in solution, salts of the various metals which are simultaneously deposited to provide the desired gold alloy plate. Included in said solution are salts of gold, palladium and one or more of the following metals: nickel, copper and cadmium. The invention will be better understood from the detailed description which follows.

Gold and palladium are compatible, precious, acidresistant metals and may be coelectrodeposited from an electrolyte under suitable conditions. When so codeposited, palladium has the property of substantially increasing the thickness of the plate for a given potential. Of course, the gold-palladium alloy plate will be acid-resistant and, as palladium is cheaper than gold, a gold-palladium alloy plate will be cheaper and longer lasting than a pure gold plate. The gold-palladium alloy plate may be further increased in thickness and the gold alloy plate rendered less costly by coelectrodepositing from the plating bath any one or more of the following metals: nickel, copper and cadmium in limited proportions so as not to adversely affect the acid-resistant and tarnish-proof characteristics of the plate.

In carrying out the invention the plating bath or electrolyte preferably contains in solution, significant amounts of salts of each of the metals which is to be coelectrodeposited to provide the alloy plate and, in practice, I have found that an exceedingly hard, lustrous, acid-resistant and tarnish-proof gold alloy plate on base metal such as brass, nickel-silver, copper and steel, which havebeen first given a flash plating of nickel, is obtainable from a bath of the following composition:

2 Water gallons" 1. Gold cyanide 0unces 0.5" Palladium chloride do 0.166 Ni'ckelcyanide do;. 0.5 Cadmium cyanide do 0.0. 3 Copper. cyanide do 0.5 Sodium chloride do 0.5 Potassium cyanide do 2.0 Potassium hydroxide do 11 In using abath'of theforegoing composition I'preferably use a potential of from four to six volts and carry out the plating operation with the bath at a temperature of approximately F.

I also prefer to use an anode of pure palladium sheet which is but slightly soluble in the plating bath but soluble to an extent sufficient to insure the proper palladium content of the bath in conjunction with the palladium chloride originally contained in the bath. Such palladium anode is superior to a stainless steel anode and cheaper than a gold anode heretofore used in gold plating.

The plating bath preferably has a pH of between 10 and 10.5 and the metals plated out of solution are periodically replaced by their respective salts in the proportions to which the bath has been depleted.

I have ascertained that the higher potential favors the deposition of the base metals while the lower potential favors the precious metals. For example, employing a bath composition as set forth above, the gold alloy plates deposited at potentials of 4 volts and 6 volts respectively, show the following analysis:

The color of the gold alloy plate may be controlled by omitting one or more of the base metal compounds from the plating bath or by changing the proportion of such metal compounds in the bath, for example, for a light yellow gold plate the proportion of the cadmium salts may be increased, while for a darker'or more copperish color gold plate the percentage of copper salts may be increased. The color is also dependent upon the temperature of the plating bath, higher temperatures favoring a deposition of a higher copper content in the alloy plate. I

In carrying out the invention any of the conventional procedures now employed in electroplating, such as barrel plating, rack'plating and wired plating, may be resorted to.

The bath composition hereinbefore recited sets forth the minimum amounts of the various elements but it will be understood that concentrations up to three times the quantities recited in said formulation may be employed in carrying out the plating operation.

While I have shown and described a novel composition of plating bath from which a plurality of precious metals and base metals may be simultaneously electrodeposited to provide a gold alloy plate which is long-wearing, acidresistant and tarnish-proof, it will be understood that I do not intend that the foregoing disclosure be considered as limitative of the invention disclosed with respect to the specific substances, proportions, potentials or temperature employed, since these may be varied without departing- Patented Oct. 4, 1955 from the spirit of my invention as defined in the appended claims.

What I claim is:

1. An electrolytic bath for depositing an acid-resistant, tarnish-proof gold alloy plate, said bath having the following composition:

Water gallons 1 Gold cyanide ounces 0.5 to 1.5 Palladium chloride do 0.166 to 0.5 Copper cyanide do 0.5 to 1.5 Nickel cyanide do 0.5 to 1.5 Cadmium cyanide do 0.05 to 0.16 Potassium cyanide do 2.0 to 6.0 Sodium chloride do 0.5,to 1.5 Potassium hydroxide do 1.0 to 3.0

2. An electrolytic bath for depositing an acid-resistant, tarnish-proof, gold alloy plate, said bath comprising essentially an alkaline aqueous solution containing gold, palladium, and at least one of the metals selected from the group consisting of copper, nickel and cadmium, and containing per gallon of water, between 0.5 and 1.5 oz. of gold cyanide, between 0.166 and 0.5 oz. of palladium chloride, and of the metals which are to be co-deposited with the gold and palladium, each as its cyanide compound, the following amounts, between 0.5 and 1.5 oz. of each of copper and nickel, and between 0.05 and 0.16 oz. of cadmium.

References Cited in the file of this patent UNITED STATES PATENTS Lambros Oct. 26, 1948 OTHER REFERENCES 

2. AN ELECTROLYTIC BATH FOR DEPOSITING AN ACID-RESISTANT, TARNISH-PROOF, GOLD ALLOY PLATE, SAID BATH COMPRISING ESSENTIALLY AN ALKALINE AQUEOUS SOLUTION CONTAINING GOLD, PALLADIUM, AND AT LEAST ONE OF THE METALS SELECTED FROM THE GROUP CONSISTING OF COPPER, NICKEL AND CADMIUM, AND CONTAINING PER GALLON OF WATER, BETWEEN 0.5 AND 1.5 OZ. OF GOLD CYANIDE, BETWEEN 0.166 AND 0.5 OZ. OF PALLADIUM CHLORIDE, AND OF THE METALS WHICH ARE TO BE CO-DEPOSITED WITH THE GOLD AND PALLADIUM, EACH AS ITS CYANIDE COMPOUND, THE FOLLOWING AMOUNTS, BETWEEN 0.5 AND 1.5 OZ. OF EACH OF COPPER AND NICKEL, AND BETWEEN 0.05 AND 0.16 OZ. OF CADMIUM. 